Switching condenser element for switching an alternating current

ABSTRACT

A condenser using a dielectric material of Pb(Zr-Ti)O3 system is used as a starting condenser for a single phase induction motor, so that the ferroelectric material is heated by an alternating current flowing through the condenser to a temperature near the Curie-point thereof and that the impedance of the condenser changes considerably.

United States Patent Kumada et ai.

[ 1 June 13, 1972 [54] SWITCHING CONDENSER ELEMENT FOR SWITCHING ANALTERNATING CURRENT [72] inventors: Akio Kumada, Kodaira; KenidchiSuzuki, Hachioji; Kenichi Kitta, Yokohama, all of Japan [73] Assignee:Hitachi, Ltd., Tokyo, Japan [22] Filed: Aug. 21, 1970 2 l App]. No.:65,995

[30] Foreign Application Priority Data Aug. 29, 1969 Japan ..44/68843[52] [1.8. CI ..3l7/230, 317/231, 317/258 [51] Int. Cl.

[58] FieldolSenrch ..3i7/238,258,23i

Primary Examiner-James D. Kailam AttorneyCraig, Antonelli & HillABSTRACT A condenser using a dielectric material of Pb(Zr-Ti)0 system isused as a starting condenser for a single phase induction motor, so thatthe ferroelectric material is heated by an alternating current flowingthrough the condenser to a temperature near the Curie-point thereof andthat the impedance of the condenser changes considerably.

9 Chins, 4 Drawing Figures SWITCHING CONDENSER ELEMENT FOR SWITCHING ANALTERNATING CURRENT BACKGROUND OF THE INVENTION 1 FIELD OF THE INVENTIONThis invention relates to a condenser for alternating current control,more particularly to a condenser using a material of Pb(Zr-Ti)0, systemas the principal ferro-electric substance or to a starting condenser fora single phase induction motor.

2. DESCRIPTION OF THE PRIOR ART As is well known in the art, a startingcondenser for a single phase induction motor is used in order to producea current which imparts the starting torque to the motor, but it isdispensable during the stationary operation time of the motor.Therefore, conventionally the condenser is disconnected by means of, forexample, a mechanical switch after it has once been started. However,such conventional method has drawbacks in that the contacts of theswitch are apt to quickly wear away because of the considerably highfrequency of operating the switch. Further, troubles are often causedby, for example, sputtering of the material of the contacts, thus makingthe life of the switch short. Though an electronic switching element maybe used in place of such mechanical switch, such electronic switchingelements are generally expensive and are not suitable for commercialmotors.

SUMMARY OF THE INVENTION One object of this invention is to provide anovel condenser for alternating current control of which the impedancedrastically changes as a result of self-heating due to an alternatingcurrent supplied to it.

Another object of this invention is to provide a condenser foralternating current control which is best suited for a startingcondenser for a single phase induction motor.

A further object of this invention is to dispense with the switch fordisconnecting the starting condenser of a single phase induction motorby using a condenser of which the principal ferro-electric material is amaterial of the Pb(2x-Ti)0, system a solid solution of PbZrO, and PbTiO,

According to this invention, to achieve the above objects, there is usedfor the dielectric material of the above described condenser a materialof Pb(Zr-Ti)0, system, or a ferro-electric material obtained by thesubstitution of a part of Pb in said system by divalent elements, forexample, rare earth elements such as Sr, Mg, Ca, Cd and Y, oralternatively a dielectric material obtained by the substitution of apart of or all of Zr or Ti in said system by such elements as Sn, Nb,Ta, P, As, Sb, Bi, Cr, W, Fe, Co and Ni, or further a dielectricmaterial of which the principal ingredient is Pblro BRIEF DESCRIPTION OFTHE DRAWINGS FIG. I is a graph showing the relation between spontaneouspolarization of a ferro-electric material and temperature.

F I68. 2 and 3 are schematic diagrams showing embodiments of thisinvention.

FIG. 4 is a circuit diagram showing a drive circuit for a single phaseinduction motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention will now bedescribed in detail in conjunction with preferred embodiments and withreference to the accompanying drawings.

The terminal voltage of a starting condenser of a single phase inductionmotor becomes higher as the motor acquires speed and the current flowingthrough it becomes greater accordingly. This current in useful only forproducing starting torque, but it is unnecessary during stationaryoperation time of the motor. That is, in order to increase the rotatingtorque while reducing the consumed power, the current must be greatlyreduced in the stationary operation time of the motor. This can beachieved by the use of a condenser of which the effective capacitancebecomes very small when the motor reaches the stationary operationstate. From this point of view, the character of a condenser foralternating current control using a ferro-electric material will beexamined hereunder.

When an AC voltage V is applied to a ferro-electric member withspontaneous polarization Ps, area S and thickness d, and the voltage israised higher than the product of the coersive electric field Ec of themember and the thickness d thereof, a hysteresis characteristic appearsin the relation between the charge Q accumulated therein and the voltagev and the admittance of the member virtually becomes considerably highbecause of the inversion of the spontaneous polarization. The relationas mentioned above can be expressed by d i V/Ec At this time the currenti following through it is given by the following formula;

idQ/dr 2PsS dZ/dr, l where Z is related to the sense of the polarizationand is in the range 1 5 Z S l. IffdZ/dt ,then i 2H8 From this relation,we can see that the current i is not dependent on the voltage Vand isproportional only to PsS.

It will be noted that the area S of the dielectric member is constantbut that Ps depends largely on temperature T as shown in FIG. 1, itbeing zero at a temperature higher than the Curie-point Tc. Within theferro-electric member, an energy of ZPsSv is lost as heat (hysteresisloss) during each cycle of the AC voltage because of the spontaneouspolarization in version as described above, with the result that itstemperature is raised to a temperature where the quantity of producedheat produced balances with that of the heat radiated.

As can be seen from the facts described above, when a condenser for ACcurrent control using a ferro-electric material is used as a startingcondenser, if the temperature of the ferroelectric material can beraised near the Curie-point by the selfheating due to said hysteresisloss by the time the motor reaches the stationary operation state, afterthe start, the expected object can be achieved.

However, if the Curie temperature of the ferro-electric material to beused is too high, it is difficult to raise the temperature by theself-heating near the Curie-point. It is also undesirable that thedifl'erence between Ps at the lowest temperature and that at the highesttemperature is too large, since in such case the temperature dependenceof the starting characteristic becomes too great. Therefore, it isnecessary to use a ferro-electric material having the Curie temperatureof about 50 c- C.

Now, TGS (tri-glycine sulphate) will be considered as one of suchferro-electric materials.

In TGS, the spontaneous polarization Ps and coersive electric field Ecare 3hr Coul/Cm] and 300[Volt/Cm], respectively, and if it is asumedthat the density of T68 is l .69, Tc is 50 C, the mean specific heat ofit over a range from 20 C to 50 C is 0.39[Cal/g.deg], V= I00 V ],f= 5050Hg], d= 0.33 [Cm] and S 53 [Cm'], then the quantity of heat Q requiredto raise its temperature from 20 C to the Curie temperature Tc is 350[Cal], while the quantity of heat Q due to the self heating is 3.75[Cal].

In ceramics of the BaTiO, SrTiO, system, I: and Be are 10 [p Coul/Cm']and 3 [K Volt/Cm], respectively, and if it is assumed that d 0.03 [Cm]and the other conditions are the same as that described above, Q and Qbecomes 36 [Joule] and 15 [Joule], respectively.

Thus, in such ferro-electric materials the diflerence between Q and Q islarge and thus it is clear that such materials are not of practical use.After all, a material of the Pb( Zr- Ti)O, system is the most suitableas the Tc thereof is near the room temperature, with a small meanspecific heat and large PSEc In FIG. 2, there is shown an example of theconstruction of a starting condenser C which is to be connected inseries with a starting winding 1 of a single phase induction motor suchas shown in FIG. 4. In FIG. 4, numeral 1 denotes a main winding, SW apower switch and P an AC power source. In the Figure, a rotor of themotor is not shown. In FIG. 2, numeral 2 denotes ceramics of thePb(Zr-Ti)O, system, 3 electrodes, 4 a

glass wool enclosure for heat insulation, 5 a heat emission case and 6terminals. It was found from a test of the characteristic of thiscondenser that in the stationary rotation time under noload, theterminal voltage Vcof the condenser was 270 V, the current Ic 60 mA andthe current ip at the power source P 270 mA.

0n the other hand, with a conventional condenser of 2 ptF connected inlieu of the above condenser, the voltage Vc was 300 V, lc 220 mA and ip350 mA. It will be seen that a considerable improvement was achievedwith the former condenser.

When the heat insulation of the condenser shown in FIG. 2 is toocomplete, it takes a long time for heat emission. 0n the contrary, ifthe heat insulation is poor, it is difficult to raise the temperatureonly by the self-heating effect. This point must be considered in orderto obtain a quick response of the motor when the power switch SW isopened or closed. One means of settling the problem is to use anauxiliary heater 7 as shown in FIG. 3. The capacity of the auxiliaryheater should be within ten times of the power (hysteresis loss)consumed by the condenser in operation time or less than 10 percent ofthe driving power of the motor. Of course, heat produced from theelement per se may be utilized to heat said ferro-electric material ifmaking the resistance of the element low by a suitable measure, forexample, by a reduction process. The condenser according to thisinvention can be used not only for a single phase induction motor butalso for similar apparatuses. In such cases, the condenser is notrequired to be necessarily made in such a structure as shown in FIG. 2or 3, but the structure known in the art may be good enough depending onthe application.

The merits of this invention will be clear from the above description,especially in that the operation characteristic of a single phaseinduction motor may be improved according to this invention, withoutusing any switching means.

We claim:

1. A condenser for alternating current control comprising a plurality ofelectrodes, a pair of terminals each connected with every other ones ofsaid electrodes, ceramics of a material of a Pb(Zr-Ti)0, system betweensaid electrodes, heat insulation means surrounding said electrodes andceramics, and a heat emission case which further surrounds the heatinsulation means.

2. A condenser according to claim I, wherein a heater is provided withinthe heat emission case.

3. A switching condenser element for switching an alternating currentcomprising a least a pair of input terminals to which an alternatingcurrent is applied, electrodes connected to said terminals and aferroelectric member substantially consisting of a solid solution ofPbZrO, and PbTiO, which is provided between the electrodes and whosethickness d is determined in accordance with the relation d a VIE whereV is a voltage applied to said member and E,- is the coercive electricfield of said member, whereby said member is heated by application ofthe alternating current to a temperature near its Curie-point and thealternating current becomes about zero at this temperature.

4. The switching condenser element according to claim 3, wherein atleast a portion of Pb in the ferroelectric member is substituted by oneof divalent metallic elements.

5. The switching condenser element according to claim 3, wherein atleast a portion of Pb in the ferroelectric member is substituted by oneof rare earth elements.

6. The switching condenser element according to claim 3, wherein atleast a portion of Zr in the ferroelectric member is substituted by anelement selected from the group consisting of Sn, Nb, Ta, P, As, Sb, Bi,Cr, W, Fe, Co, and Ni.

7. The switching condenser element according to claim 3, wherein atleast a portion of Ti in the ferroelectric member is substituted by anelement selected from the group consisting of Sn, Nb, Ta, P, As, Sb, Bi,Cr, W, Fe, Co, and Ni.

8. The switching condenser element for switching an alternating currentaccording to claim 3, which further com rises heat insulation meanssurrounding said electrodes an said member, and a heat emission casewhich further surrounds the heat insulation means.

9. The switching condenser element according to claim 8, wherein aheater is provided within the heat emission case.

Q i Q I

2. A condenser according to claim 1, wherein a heater is provided withinthe heat emission case.
 3. A switching condenser element for switchingan alternating current comprising a least a pair of input terminals towhich an alternating current is applied, electrodes connected to saidterminals and a ferroelectric member substantially consisting of a solidsolution of PbZrO3 and PbTiO3 which is provided between the electrodesand whose thickness d is determined in accordance with the relation d <or = V/Ec where V is a voltage applied to said member and Ec is thecoercive electric field of said member, whereby said member is heated byapplication of the alternating current to a temperature near itsCurie-point and the alternating current becomes about zero at thistemperature.
 4. The switching condenser element according to claim 3,wherein at least a portion of Pb in the ferroelectric member issubstituted by one of divalent metallic elements.
 5. The switchingcondenser element according to claim 3, wherein at least a portion of Pbin the ferroelectric member is substituted by one of rare earthelements.
 6. The switching condenser element according to claim 3,wherein at least a portion of Zr in the ferroelectric member issubstituted by an element selected from the group consisting of Sn, Nb,Ta, P, As, Sb, Bi, Cr, W, Fe, Co, and Ni.
 7. The switching condenserelement according to claim 3, wherein at least a portion of Ti in theferroelectric member is substituted by an element selected from thegroup consisting of Sn, Nb, Ta, P, As, Sb, Bi, Cr, W, Fe, Co, and Ni. 8.The switching condenser element for switching an alternating currentaccording to claim 3, which further comprises heat insulation meanssurrounding said electrodes and said member, and a heat emission casewhich further surrounds the heat insulation means.
 9. The switchingcondenser element according to claim 8, wherein a heater is providedwithin the heat emission case.